It is estimated that one in four citizens of developed nations will experience a mental health problem during their lifetime, with up to 10 percent of the population experiencing some type of depressive or anxiety-related disorder every year. The global economic cost of mental illness is measured in trillions of dollars annually.
Presently, there is no accepted and widely recognised objective test for many mental illnesses, such as depression. The diagnostic ‘gold standard’ in such cases remains clinical/expert assessment and opinion, based upon interviews with the patient along with close friends and family, and self-reporting (e.g. through the completion of questionnaires), for comparison against clinical symptoms catalogued in the Diagnostic and Statistical Manual of Mental Disorders (currently DSM-5).
However, due to the subjective nature of many aspects of this diagnostic process, agreement between clinicians can vary considerably, even for high-prevalence disorders such as depression and anxiety.
There is, accordingly, a need for quantitative, objective tests that can be employed by clinicians when diagnosing psychological disorders, and for monitoring the progress of patients undergoing treatment. Ideally, such tests should be simple, safe and unobtrusive, so that they can be undertaken without significant impact on the patient's lifestyle or day-to-day routine.
Provision of objective tests for mental health would enable numerous significant benefits to be realised. Better objective information could lead to earlier diagnosis, earlier intervention, and better outcomes for patients. Ongoing monitoring of patients could provide an objective indication of therapeutic effectiveness, enabling treatments to be varied and optimised based upon patient response. These improvements in treatment and outcomes would result in savings to the health system, and to the community in general.
It has been known for some time that there is a relationship between circadian heart rate patterns and psychological state. For example, U.S. Pat. No. 6,245,021 describes the use of recorded 24-hour heart rate patterns in the diagnosis of psychological disorders including depression, anxiety, panic disorder, obsessive compulsive disorder (OCD) and schizophrenia. However, the procedures disclosed in this patent still require expert (i.e. human) review of circadian heart rate patterns, by clinicians with the necessary training and experience to identify features that are commonly associated with the different disorders. Patients are required to maintain a daily diary, which enables the clinician to compare features in the heart rate patterns against activity (e.g. exercise) in which the patient may have engaged, so as to avoid misinterpreting these features. Clearly, a system that requires 24-hour monitoring, and the keeping of a daily diary, has a noticeable impact upon the patient's lifestyle and day-to-day routine, leading to a greater likelihood of non-compliance with the measurement and monitoring regime.
Accordingly, it would be desirable to develop new and objective methods and systems to assist in identifying individuals who may be suffering from, or at risk of, adverse mental health conditions such as depression, and which are able to provide one or more of the benefits discussed above. The present invention has been devised in order to address this need.